What @BandOfBrothers has suggested will stop the SIM being used, but your Google account will still be on the phone. You can remove that remotely by signing into your Google account on a pc. Go to Account, then Security and Devices. Under Manage Device, there's the option to remove account access. If you find the phone again, you'll need to sign in, but I don't know whether you'll also need to set everythign up from scratch.
If the device is permanently lost, you can get a replacement SIM. Activate this and the old one will cease to work.
